Genome analysis of Lotus japonicus

The state of genome analysis for Lotus japonicus, a model legume plant, was reviewed and compared with Medicago truncatula and soybean. Several mutant libraries are being analyzed, focusing on the nodulation mechanism. The first plant nodulation gene nin was cloned by Ac-transposon tagging, Soybean remains as the most studied legume, especially in relation to the disease resistance genes. However, Lotus japonicus offers several advantages for molecular genetics, and the remained lackings were recently filled up, namely 1) an appropriate crossing partner for Gifu, accession Miyakojima, was proposed for its 4% polymorphism and smooth recombining ability; 2) a genome library with long inserts, average of 140 kb, and 8.2 genome equivalents of library size, has been established; and 3) the rather low polymorphic rate between Gifu and Miyakojima can be overcome with the HEGS (High Efficiency Genome Scanning). With this infrastructure, positional cloning of the causative genes of several mutant libraries will be accomplished in a short term. Genome sizes of L. japonicus acc. Gifu and Miyakojima were determined with high accuracy, to be 494+/-0 MB and 512+/-1 MB, respectively. The feasibility of constructing a physical map of the entire genome, for functional genomics, was discussed.